The invention relates to adhering rubber to tire cord reinforcement in a component of a vehicular tire.
Pneumatic rubber tires are conventionally prepared with rubber components which can be a blend of various rubbers which is typically reinforced with a reinforcing pigment such as carbon black.
In one aspect, it is desired to provide rubber compositions which maintain good adhesion to reinforcing tire cord, which is typically in a form of fiber, or fabric, reinforcement, particularly wire reinforcement. A rather conventional method in promoting adhesion between rubber and such fiber reinforcement is to pretreat the reinforcing fiber with a mixture of rubber latex and a phenol/formaldehyde condensation product, or resin, in which the phenol is usually resorcinol. This is often referred to as the "RFL" (resorcinol-formaldehydelatex) method. An alternative method of promoting such adhesion is to form the resin in-situ (in the vulcanized rubber/fiber matrix) by blending the phenol/formaldehyde condensation product (referred to herein as the "in-situ" method).
The components of the condensation product consist of a methylene acceptor and a methylene donor. The most common methylene donors include N-(substituted oxymethyl) melamine, hexamethylenetetramine or hexamethoxymethylmelamine. A common methylene acceptor is a dihydroxybenzene compound such as resorcinol. The in-situ method has been found to be particularly effective where the reinforcing material is steel wire since pretreatment of the wire with the RFL system has been observed to be largely ineffective.
An example of the use of methylene acceptor and methylene donor system may be found in U.S. Pat. No. 3,517,722.
Resorcinol is known to form a resin network within a rubber polymer by reacting with various methylene donors. Unfortunately, the use of resorcinol has some inherent disadvantages. Resorcinol is not readily dispersed in rubber and in fact neither the resin, nor the resorcinol become chemically bound to the rubber. Additionally, resorcinol in its raw form is excessively volatile and is potentially an environmental hazard.
In one aspect it is considered that the resorcinol-formaldehyde acts to beneficially stiffen the rubber composition surrounding the cord reinforcement while the melamine, or tetramine acts to enhance the adhesion of the rubber to the cord, particularly on an aged adhesion basis.
There have been various attempts to replace resorcinol in such a rubber component. However, few if any have had significant success. For example, in U.S. Pat. No. 4,605,696 there is disclosed a method for enhancing adhesion of rubber to reinforcing materials through the use of phenolic esters as the methylene acceptor.
Therefore, there exists a need, or desire, to find, or implement, a suitable resorcinol replacement for use in various tire components.
U.S. Pat. No. 4,513,123 discloses a rubber composition of dithiodipropionic acid with natural rubber, or blends of natural and synthetic rubbers, 30-80 parts carbon black, sulfur and organo-cobalt compound for use as a skim coat for brass-plated steel, It relates that the rubber composition can contain other additives such as fillers such as clays, silicas or calcium carbonate, process and extender oils, antioxidants, cure accelerators, cure activators, cure stabilizers and the like.